Hydrocyanation catalyst systems, particularly pertaining to the hydrocyanation of ethylenically unsaturated compounds, are known in the art. For example, systems useful for the hydrocyanation of butadiene to form pentenenitrile (PN) and in the subsequent hydrocyanation of pentenenitrile to form adiponitrile (ADN), are known in the commercially important nylon synthesis field.
The hydrocyanation of ethylenically unsaturated compounds using transition metal complexes with monodentate phosphite ligands is documented in the prior art. See, for example, U.S. Pat. Nos. 3,496,215; 3,631,191; 3,655,723; and 3,766,237, and Tolman et al., Advances in Catalysis, 1985, 33, 1. The hydrocyanation of activated ethylenically unsaturated compounds, such as with conjugated ethylenically unsaturated compounds (e.g., butadiene and styrene), and strained ethylenically unsaturated compounds (e.g., norbomene) proceeds without the use of a Lewis acid promoter, while hydrocyanation of unactivated ethylenically unsaturated compounds, such as 1-octene and 3-pentenenitrile, requires the use of a Lewis acid promoter.
Teachings regarding the use of a promoter in the hydrocyanation reaction appear, for example, in U.S. Pat. No. 3,496,217. This patent discloses an improvement in hydrocyanation using a promoter selected from a large number of metal cation compounds with a variety of anions as catalyst promoters. U.S. Pat. No, 3,496,218 discloses a nickel hydrocyanation catalyst promoted with various boron-containing compounds, including triphenylboron and alkali metal borohydrides. U.S. Pat. No. 4,774,353 discloses a process for the preparation of dinitriles, including ADN, from unsaturated nitriles, including PN, in the presence of a zero-valent nickel catalyst and a triorganotin catalyst promoter. Moreover, U.S. Pat. No. 4,874,884 discloses a process for producing ADN by the zero-valent nickel-catalyzed hydrocyanation of pentenenitriles in the presence of a synergistic combination of promoters selected in accordance with the reaction kinetics of the ADN synthesis.
Phosphite ligands have been shown to be useful ligands in the hydrocyanation of activated ethylenically unsaturated compounds. See, for example, Baker, M. J., and Pringle, P. G., J. Chem. Soc., Chem. Commun., 1991, 1292; Baker et al., J. Chem. Soc., Chem. Commun., 1991, 803; Union Carbide, WO 93,03839. Also, phosphite ligands have been disclosed with rhodium in the hydroformylation of functionalized ethylenically unsaturated compounds: see, Cuny et al., J. Am. Chem. Soc., 1993, 115, 2066.
U.S. Pat. No. 5,512,696, which issued Apr. 30, 1996, discloses processes and catalyst compositions for the hydrocyanation of monoethyleneically unsaturated compounds using zero-valent nickel and certain multidentate phosphite ligands, and Lewis acid promoters, which are similar to those encompassed by the present invention, except for the choice of the ortho substituent for the group or the phosphite phenyl termini.
Like U.S. Pat. No. 5,512,696, the present invention provides processes and catalyst precursor compositions which are more rapid, selective, efficient and stable than prior processes and catalyst complexes employed in the hydrocyanation of monoethylenically unsaturated compounds. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the detailed description of the invention which hereinafter follows.